Research on the development and self-assembly of dissociated embryonic neural tissues reaggregated in rotary cultures will be continued along two main directions. On one hand, Golgi analyses of aggregates prepared from dissociated and embryonic chick and mammalian cortices will be extended to very early embryonic stages to ascertain the development of neuronal phenotypes and their pattern of assembly. On the other hand critical experiments will be performed to further substantiate the immunological nature of a special type of cell apposition observed among embryonic neurons developing in situ.